Question

page 74 Exp. 9: Acid-Base Titration Questions (show your work for the math problems!) Write a balanced equation as in footnote 2 for the neutralization of formic acid with sodium hydroxide. 1. H-C-OH Formic acid If an air bubble is t initially in the tip of the vinegar buret, but disappears' during the 2. course of the titration, how would this affeet your calculation for the concentration of (larger, smaller, no effect)? Explain your answer. Explain how the indicator phenolphthalein works. Why does it turn pink only when nsue-nN H? 3. 4. Using a pipet, 20.00 mL of acetic acid is titrated with 0.2000 M solution of NaOH. The initial reading in the NaOH buret is 1.12 mL. When the solution is very light pink, the buret reads 24.37 mL. what is the concentration of acetic acid both in M and in % 5. Remembering that sulfuric acid (H SO) is a diprotic acid (i.e., has two acidic H's) write the equation for its neutralization reaction with NaOH. How many mL of a 0.200 M solution of NaOH would be required to neutralize 25.00 mL of a 0.100 M solution of sulfuric acid?

Answer 1

2. We can easily carry out the titration with presence of bubble also if it does not escape the burette. If it escapes out, then some volume will remain unknown which was covered by the bubble. So the bubble will decrease the concentration of acetic acid up to a very small extent only.

3. For Acid-Base titrations, certain kind of indicators are used to determine the pH of the equivalence point which concide with the pH range of indicator. Thus the pH range of phenolphthalein lis about 8.3-10.0 so it can be used for the titration of strong bases with strong acids as well as strong bases with weak acids.

Phenolphthalein is a weak acid in nature. The weak acid is colourless and its conjugate acid is bright pink. Thus according to le chatleir principle , addition of hydrogen ions will shift the position of the equilibrium towards left turning the indicator colorless ad adding more of hyrdoxide ions will remove or neutralize the hydrogen shifting the equlibrium towards left and turning the indicator pink.

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